(a) Field of the Invention
The present disclosure relates to a purification method of a photoreactive compound, and a photoreactive compound. More particularly, the present disclosure relates to a method of purifying a light and heat-sensitive photoreactive compound in high purity by molecular distillation.
This application is a National Stage Application of International Application No. PCT/KR2014/007139, filed on Aug. 1, 2014, which claims the benefit of Korean Patent Application No. 10-2013-0091892, filed on Aug. 2, 2013 and Korean Patent Application No. 10-2014-0098440, filed on Jul. 31, 2014, all of which are hereby incorporated by reference in their entirety for all purposes as if fully set forth herein.
(b) Description of the Related Art
In recent years, as a liquid crystal display has become bigger, its application has been expanded from personal mobile phone or notebook computer to home wall-mounted television, and thus it is required to ensure the high definition, the high quality, and the wide viewing angle in respects to the liquid crystal display. In particular, since a thin film transistor liquid crystal display (TFT-LCD) driven by a thin film transistor independently drives each of pixels, a response rate of the liquid crystal is very high, and thus a high-quality dynamic image can be realized. Accordingly, the application range thereof is expanded.
In order to use liquid crystals as an optical switch in the TFT-LCD, liquid crystals needs to be initially oriented in a predetermined direction on a thin film transistor, which is disposed in the most inner portion of a display cell. For this purpose, a liquid crystal alignment film is used.
To achieve the liquid crystal alignment in liquid crystal displays, a rubbing process of aligning liquid crystals by rubbing an alignment film, or a process of aligning liquid crystals by light (hereinafter, referred to as “photoalignment”) has been used until now.
The photoalignment refers to a mechanism, in which a photosensitive group connected to a polymer generates a photoreaction due to linearly polarized UV, and in this procedure, a main chain of the polymer is unidirectionally aligned, thereby forming a photopolymerizable liquid crystal alignment film in which the liquid crystals are aligned.
A representative example thereof is a photoalignment by photopolymerization, which is announced by M. Schadt, et al. (Jpn. J. Appl. Phys., Vo131, 1992, 2155), Dae S. Kang, et al. (U.S. Pat. No. 5,464,669), and Yuriy Reznikov (Jpn. J. Appl. Phys. Vol. 34, 1995, L1000).
In these patent documents and papers, polycinnamate-based polymers such as PVCN (poly(vinyl cinnamate)) and PVMC (poly(vinyl methoxycinnamate)) are generally used as the photoalignment polymers. In the case of performing the photoalignment, the cycloaddition reaction [2+2] of the double bond [2+2] of cinnamate forms cyclobutane by UV, and thus an anisotropic property is formed to unidirectionally align liquid crystal molecules, leading to the alignment of the liquid crystals.
With regard to the known photoalignment polymers, Japanese Patent Laid-open Publication No. Hei11-181127 discloses a method of manufacturing a polymer-type alignment film including a main chain such as acrylate and methacrylate and a side chain containing a photosensitive group such as a cinnamate group, and an alignment film manufactured thereby. However, in this case, the polymer main chain has a poor thermal stability so that it has a negative impact on the stability of the alignment film. Also, it is not easy to control a photoreaction rate via cinnamate substituent groups.
To prepare the photoalignment polymer having excellent performances, a high-purity photoreactive compound is needed as a monomer. However, since the photoreactive compound is sensitive to light and heat and has a property of high boiling point, it is not easy to purify the photoreactive compound in high purity.